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Abstract

In contrast to animals, plants develop mostly postembryonically and continuously form new organs during their entire life cycle. The cellular basis for this mode of development is the continuous presence of stem-cell pools in the apical meristems of shoot and root, which are the growing points of a plant. The size of the stem-cell pool has to be tightly regulated to avoid ill effects for the organism. In Arabidopsis thaliana, several key factors of stem cell control have previously been identified by genetic approaches. Since most of them are transcription factors, we have set out to elucidate the regulatory network of stem-cell control by means of transcriptional profiling. Focusing on the shoot apical meristem and the floral meristem, we have used loss-of-function mutants, as well as inducible overexpression lines of several key factors including WUSCHEL (WUS), CLAVATA3 (CLV3) and LEAFY (LFY) to identify common and unique targets. By conducting meta-analysis on our expression data and screening for transcripts that follow the genetically defined regulatory logic, such as the negative feedback loop between WUS and CLV3, we were able to identify several high priority targets. Promoter regions of these targets are used for regulatory element searches, with the aim to identify previously unknown sites. Currently we verify the microarray data by quantitative rtPCR and study their spatial expression domains and dynamics by in situ hybridization. Furthermore, we use chromatin immunoprecipitation techniques to study the interaction of the transcription factor WUS with its target genes in vivo. With these diverse approaches we hope not only to gain insight into the in vivo function of target genes, but also into the regulatory logic of stem-cell control. Ultimately, we want to establish a comprehensive model of stem cell homoeostasis with predictive power.